Abstract

CUMS + PCPA male mouse model replicates comorbid depression and insomnia. • Lemborexant and fluoxetine reduce depressive- and anxiety-like behaviors. • Both drugs normalize hypothalamic–pituitary–adrenal (HPA) axis hyperactivity. • Lemborexant improves sleep continuity and consolidates NREM and REM sleep. • Findings support dual orexin receptor antagonism as a strategy for depression with insomnia. Stress is a well-established precipitant of major depressive disorder (MDD), frequently co-occurring with sleep disturbances, creating a pressing need for therapies that can concurrently alleviate affective and sleep symptoms. First-line antidepressants like the selective serotonin reuptake inhibitor SSRI fluoxetine (FLX) alleviate mood symptoms but often fail to address sleep disturbances and may even disrupt sleep architecture. The orexin system, a central regulator of sleep-wake stability and emotional processing, represents a promising target for treating comorbid depression and insomnia. Here, we investigated the effects of the dual orexin receptor antagonist (DORA) lemborexant (LEM) relative to FLX in adult male ICR mice using a depression-insomnia model induced by chronic unpredictable mild stress (CUMS) combined with para-chlorophenylalanine (PCPA, a serotonin synthesis inhibitor that induces insomnia-like phenotypes). Both drugs alleviated depressive- and anxiety-like behaviors and normalized hypothalamic–pituitary–adrenal axis (HPA) hyperactivity. However, they exerted fundamentally different effects on sleep: LEM consolidated sleep by prolonging non-rapid eye movement (NREM) and rapid eye movement (REM) sleep bout durations, whereas FLX increased sleep–wake fragmentation. Notably, improvements in REM sleep continuity were strongly associated with affective recovery. Together, these findings indicate that LEM exerts antidepressant- and anxiolytic-like effects while modulating sleep in a comorbid depression–insomnia model, providing preclinical evidence for DOR